EXAMINATION OF WATEE 



397 



growth of the typhoid bacillus, while in the presence of 

 0'l4i per cent, it will not develop at all. He further states 

 that in the presence of small quantities of phenol the colon 

 bacillus presents stronger resemblances to the typhoid 

 bacillus than usual. 



To ascertain if the resisting power of cultures of the 

 B. typhosus to phenol differed, we tried the following series 

 of experiments on different cultures of the organism, using 

 varying percentages of phenol, with the following results : 



Thus, it is seen that the resisting power of the B. typhosus 

 to phenol varies with different cultures. The sample marked 

 (a), which was freshly isolated from the dejecta from a 

 typhoid case, had less resisting power than other samples 

 which had been subcultured through many generations. 



Parietti proposed the use of broth containing both phenol 

 and hydrochloric acid to eliminate the common water 

 organisms. He takes advantage of the fact that the 

 typhoid and colon bacillus will grow in a slightly acid 

 medium, whereas the majority of other organisms will not. 



Parietti's method is as follows : The following solution is 

 prepared : Five grammes of phenol and 4 grammes of pure 

 hydrochloric acid are added to 100 c.c. of distilled water. 

 From O'l to 0'3 c.c. of this solution is added to a series of 

 test-tubes containing 10 c.c. of sterile nutrient broth ( = 0"05 

 to 0*15 per cent, of phenol). The tubes are then incubated 

 at blood-heat for twenty-four hours, to destroy any stray 

 organisms that may have gained access to the tubes. From 



